The invention relates to a hot runner feed system (also called hot runner gating system or hot runner sprue system) for a diecasting mold, wherein the feed system includes a melt manifold and feed block construction having an entry-side feed inflow opening, at least one first and one second exit-side feed outflow opening which open into a mold separation plane between a fixed mold half and a movable mold half of the diecasting mold, and a casting runner-duct structure that extends so as to branch out from the feed inflow opening to the feed outflow openings.
A hot runner feed system by the applicant, having the trade name Frech-Gießlauf-System, or Frech-Gating-System (FGS), respectively, for diecasting molds, such as is also mentioned, for example, in the magazine essay Druckgießen (Diecasting) by L. H. Kallien and C. Böhnlein, Gießerei 96, 07/2009, pages 18 to 26, is commercially available. In general, hot runner feed systems as compared to other conventional feed systems have the advantage that the proportion of melt material which is allocated to the so-called ingate, or to the ingate region that is upstream of the mold cavity, respectively, and has to be severed from the cast casting, can be significantly reduced.
Hot runner feed systems by the applicant, which are, for example, of a comb-type or fan-type feed, or have dedicated feed block units having an integrated melt runner heating that are insertable into a respective mold, are disclosed in patent publications EP 1 201 335 B1 and EP 1 997 571 B1.
More recently, the demand for diecasting molds and associated feed systems which operate in a relatively high temperature range of up to approx. 750° C. has grown. At this elevated temperature, the risk of an undesirable formation of oxide and the risk of fire in the case of highly reactive and intensely oxidizing melts such as magnesium is increased in particular in exit opening regions of the feed system. A direction of approach for addressing these problems lies in a transition from comb and fan feed systems to systems having a fewer number of casting outflow openings that are of a larger dimension.
The layout of the hot runner feed system for said elevated temperature range compounds the difficulties which are associated with the thermal expansion of various components of the feed system and of the components that surround the latter, in particular of the adjacent parts of the fixed mold half and of the movable mold half. In particular, differences in the thermal expansion by virtue of the use of different materials for the respective components are also to be taken into account here. At the same time attention has to be paid to a reliable sealing of the feed system in order to prevent melt leakages by virtue of the lack of tightness in the system. Conventional seals such as used in hot runner systems of the mold construction for plastic injection molding that are conceived for a lower operating temperature range are not well suited to the elevated operating temperature range mentioned, not least because the seals not only have to reliably seal in the operating temperature range when the melt-conducting runners are at the liquidus temperature, but also have to survive the cooling process of the casting procedure when the system is still filled with melt and the latter solidifies as it cools in the runner.
In order for these problems to be overcome, the geometry and the temperature profile of the hot runner feed system are chosen such that the melt exits are preferably disposed so as to ascend and that a temperature gradient is set from a hot upstream region which is formed, for example, by a melt manifold region and depending on the melt material used is kept at an operating temperature of, for example, 380° C. to 700° C., to a less hot downstream region which is adjacent to a contour-imparting part of the mold that is formed by the fixed and by the movable mold half, having an operating temperature range of approx. 120° C. to 300° C. The temperature conditions described reinforce the range of problems in the thermal expansion of dissimilar and mutually adjacent system components.
Patent publication DE 10 2005 054 616 B3 discloses a permanent diecasting mold having a casting-die element that at least partially surrounds a mold cavity, and a diecasting mold insert which has an upper side that is assigned to the mold cavity, a basic element which in the case of a cold diecasting mold by way of a clearance sits in a receptacle of the casting-die element, and a supporting collar which in a form-fitting manner sits in a step of the receptacle that transitions to the mold cavity. An overall height of the supporting collar and of the basic element, by an undersize that is at least equal to a height dimension by way of which the basic element expands in the direction of height during casting, is smaller than a depth of the receptacle.
Patent publication DE 840 905 discloses an injection casting mold in which part of a mold cavity is disposed in an insert which is displaceable in the direction of the mold partition so that said insert can be centered in a self-acting manner in relation to an ejection mold, to which end the latter has a recess which fits into an end of the insert.
It is an object of the invention to provide a hot runner feed system of the type mentioned at the outset which in terms of process reliability is also advantageously suitable for comparatively high diecasting temperatures.
The invention achieves this and other objects by providing a hot runner feed system in which the melt manifold and feed block construction at least in an exit-side block region that includes the two or more feed outflow openings in a transverse direction parallel with the mold separation plane in relation to a predefined nominal operating extent is made so as to be shortened by an expansion dimension which has been predefined as the thermal transverse expansion of this block region when heated from a room temperature range to a predefined operating temperature range that is elevated in relation to said room temperature range. The thermal transverse expansion herein is understood to be a relative size, that is to say relative to a potential smaller thermal transverse expansion of neighboring system components such as, in particular, of a neighboring region of the fixed mold half.
By way of this measure according to the invention, the longitudinal expansion of the melt manifold and feed block construction is considered in a controlled manner in the particularly relevant exit-side region, said controlled manner including a pre-determination of the associated thermal expansion. The pre-determination can be performed by experiments and/or by means of a computed simulation as is known per se to a person skilled in the art, wherein the respective influence parameters represent input variables of this pre-determination and represent the respective diecasting mold observed, together with the parts relevant to the latter.
When the melt manifold and feed block construction is heated from room temperature to operating temperature, said melt manifold and feed block construction expands by precisely the expansion dimension by which the former has been made in a shortened manner, such that said melt manifold and feed block construction, in particular also by way of the exit-side block region thereof that includes the feed outflow openings, matches the adjacent system components, for example of the fixed mold half, in a gap-free and sealing manner. The sufficient tightness at the contact/connection points is preferably achieved by suitable material pairings in such a manner that the dissimilar coefficients of thermal expansion seal the system more tightly as the temperature increases. To this end, depending on the type of application, suitable temperature-dependent pretensions can be pre-computed and applied, and/or conical sealing faces can be utilized in the temperature range of the tool. The invention thus enables a diecasting-tight connection between the melt manifold and feed block construction on the one hand, and the fixed mold half, on the other hand, that is to say a connection that is sufficiently tight in relation to the diecasting melts, to be provided, without dedicated sealing elements having to be inevitably used to this end.
In one refinement of the invention, the melt manifold and feed block construction has an integral manifold and feed block that includes the casting runner-duct structure from the feed inflow opening up to the feed outflow openings and comprises the exit-side block region. This refinement in terms of the construction is advantageous in particular for systems having comparatively smaller dimensions and/or lower operating temperatures. On account of the integral construction, contact points to be sealed between a melt manifold region and a feed system region that adjoins the former at the exit side are dispensed with.
In one embodiment, the exit-side block region in the case of this integral manifold and feed block forms an elongate oval, in each case one feed outflow opening being located in the two end regions of said oval.
In another embodiment, the exit-side block region of this integral manifold and feed block is insertable into a receptacle of the fixed mold half, wherein the receptacle has a transverse extent that corresponds to the nominal operating extent of the exit-side block region.
In one refinement of the invention, the melt manifold and feed block construction has a melt manifold block that includes the entry-side feed inflow opening, and adjacent thereto a first feed block that includes the first feed outflow opening and a second feed block that includes the second feed outflow opening. In each case one feed insert which is on the fixed mold half so as to be displaceable in a transverse direction that is parallel with the mold separation plane and so as to be fixable to said fixed mold half is disposed on the first and on the second feed block. The respective system components in a state in which the former have not yet been heated to the operating temperature and are not fixed can be displaced in relation to one another, so as for said system components to be fixed to one another once the desired operating temperature range has been reached. The longitudinal expansion effects that are caused by the heating procedure can thus be absorbed. The tightness in the operating temperature range can be ensured by said fixing. Any existing intermediate spaces can optionally be covered or sealed, respectively, by an associated cover plate.
In one embodiment of this measure, the feed inserts are in each case assigned one wedge plate for bracing the feed inserts by wedging on the fixed mold half. This in terms of construction represents an advantageous method for fixing the feed inserts to the fixed mold half. In a further design embodiment, the feed inserts are displaceable along a connecting line of the first and the second feed outflow opening, and are capable of being braced by the wedge plates in a transverse direction that is perpendicular to said connecting line.
In one refinement of the invention, the melt manifold and feed block construction has a melt manifold block having a first exit nozzle that is assigned to the first feed outflow opening, and a second exit nozzle that is assigned to the second feed outflow opening, and an intermediate plate having nozzle fitting mouthpieces for fitting the exit nozzles in a centering manner. The intermediate plate herein is made having a mutual spacing of the nozzle fitting mouthpieces thereof that corresponds to an operating temperature spacing of the exit nozzles, while the melt manifold block is made having a spacing of the exit nozzles thereof that corresponds to a room temperature spacing that is smaller in comparison to the operating temperature spacing. This in terms of construction represents an advantageous implementation in particular also for systems having comparatively larger dimensions and higher operating temperatures, and an alternative to the implementation by way of displaceable and fixable feed inserts.
The intermediate plate by way of the nozzle fitting mouthpieces thereof represents the released position of the system in the so-called run-out position of the diecasting mold. The intermediate plate, after having been heated to the operating temperature, can be run on to an existing heating pack and onto the exit nozzles of the melt manifold block, on account of which said intermediate plate can brace and seal the exit nozzles. The intermediate plate thereafter can be arrested, whereupon the tool operates in this configuration until the operating temperature range is departed from again.
Advantageous embodiments of the invention are illustrated in the drawings and will be described hereunder. In the drawings: